1. Field of the Invention
The invention relates to temperature management systems for people aids and in particular to devices for therapeutically cooling.
2. Description of the Prior Art
The human body is constantly producing heat when metabolizing food. This heat is an import part of bodily function but too much can be detrimental. The body expels extra heat to ambient environment in a variety of ways such as: convection, radiation, and evaporation. All of these ways can be hindered by a thermally insulating material such as the foam padding used in chairs or bedding pressed up against the body trapping in heat. The inability to expel this heat can at first cause the person to become uncomfortable but if the heat continues to build up it could cause severe health effects.
U.S. Pat. No. 5,372,608 to Johnson (1994) is a therapeutic device for chilling a body joint. It is mostly comprised of a flexible container with an inlet port and an outlet port, a tubing system and a reservoir with an inlet and outlet port. When a chilled liquid is added to the reservoir, which is positioned above the flexible container, gravity forces the liquid out of the outlet through the tubing system and in to the flexible container. The flexible container is worn against a persons body part to be chilled where it is warmed up by absorbing heat from the person. The warmed liquid becomes more buoyant and thus flows out of the flexible container up the tubing and back in to the reservoir via its inlet port completing the cycle. This process will continue until the temperature of the chilled liquid rises to the body temperature of the person and can not absorb any more heat energy. This system does not have a means of expelling the heat to the ambient environment.
U.S. Pat. No. 5,562,604 to Yablon (1996) is a portable therapeutic device for treating a patient undergoing hot or cold therapy. This device is comprised of a flexible containment bag means comprising a sealed closed-loop fluid channel containing a liquid, an electromagnetic pumping means, a self-contained source of a therapeutic temperature and microprocessor temperature control. While this device is configured for cooling the flexible containment bag is warn against the person receiving the therapy. Heat is transferred from the person to the bag, which contains the liquid. The liquid receives the heat and rises in temperature. The heated liquid is pumped through the channels using an electromagnetic pump to the self-contained source of therapeutic temperature control. The temperature control unit then removes the heat from the liquid. This portable therapeutic device relies on an electromagnetic pump to move the liquid. Electromagnetic pumps require that the liquid it pumps be a good electrical conductor.
U.S. Pat. No. 6,770,085 to Munson (2004) is a thermal absorbing pad comprising a bladder made of an elastomer material, a thermoelectric cooling unit, a fluid with a boiling point lower than room temperature at 1 atmosphere of pressure and a tube. The bladder and the tube contain the fluid. The tube connects the bladder to the cooling unit and act as a heat pipe to transfer evaporated fluid from the bladder to the cooling unit and condensed fluid from the cooling unit to the bladder. The bladder enclosing a spongy pad and a fluid is where the heat absorption takes place. This heat is transferred to the fluid converting it in to a vapor. The tube conveys the vapor to a cooling unit. A cooling unit than condenses the vapor back into a liquid using a thermoelectric module to remove the heat. This thermal absorbing pad must use a fluid with a boiling point below the body temperature of the person using it in order for it to cool the person.
All of the aforementioned devices have the ability to therapeutically cool a person. Each one has it's own method of accomplishing basically the same thing. Likewise each method has strengths and limitations. The Johnson device is a purely passive device that only cools until it has absorbed all the heat it can handle much like an icepack. It lacks the ability to keep itself cool indefinitely. The Yablon device has the ability to cool the person for as long as the system has power but it has to actively use a pump to move the cooled liquid to the person. The Munson device has the ability to cool the person indefinitely and does not require the use of a pump to actively move the cooling medium to the person. However the cooling medium must be a refrigerant with a boiling point below the temperature of the person. These types of refrigerants are often expensive, have negative impacts on the environment, dangerous and are hard to work with.